[AlphAcorn (OP)]

The meteor that collided with Earth, was it a meteor or a comet? but say if a fairly large comet came into the path of Earth's orbit, would it not have been able to reflect solar radiation onto the planet as say it is affected by Earth's gravity, and to what extent, would it be hot enough to burn most vegetation? Could that have been a major factor in the demise of the dinosaurs?

[evan_au]

That is thought to be the nature of the Chicxulub crater in Mexico.
The impact would have been severe enough to set all vegetation alight, planet-wide, within an hour or two (this is much faster than the speed of sound).
Only seeds and animals that were underground, underwater or in deep snow would have survived.
This event (perhaps coupled with near-simultaneous volcanic eruptions in the Deccan traps in India) caused the extinction of the dinosaurs.

https://en.wikipedia.org/wiki/Chicxulub_crater

[evan_au]

meteor or a comet... reflect solar radiation onto the planet ... would it be hot enough to burn most vegetation

No...
Meteors have a very small size - it is thought that the one that created Chicxulub was around 10-15km across. This would have reflected so little light from the Sun that it would not have been visible at night without a telescope even 1 day before impact. Reflected sunlight would not have affected the Earth at all - much less than a small cloud in the sky.

Comets are far more visible, with the gas and dust in their tails often stretching to 1 million km in length. Large comet tails are often visible as they round the Sun, just before dawn, or just after sunset. If there were naked-eye astronomers back then, they probably saw this comet at some point in its orbit around the Sun. However, the tail of the comet is a really thin veil that is invisible when the Sun is up. Again, the tail of the comet would reflect less light than a small cloud in the sky. In historical times, the Earth has passed near or through the tail of major comets, with no more impact than a good meteor shower.

We can't really tell if the object that killed the dinosaurs was a meteor or a comet - we now think of them as a spectrum, ranging from very icy comets, to rocky meteors, and a variety of icy+rocky bodies in between.

However, when it hit the Earth's atmosphere, it would have turned into a searing fireball, easily visible in daylight.
- This would have ignited vegetation directly under the entry path
- Upon impact, the shockwave would have moved outward at slightly more than the speed of sound, knocking over and igniting vegetation
- It struck the sea, setting off massive tsunamis
- It released sulphate chemicals into the atmosphere which would have affected the weather
- it is thought that rock would have been vaporised and blasted back into space, raining down over the whole planet in the next hour, making it a global catastrophe
- The link to the Deccan Traps (if any) is the subject of speculation. But massive volcanic eruptions would not have helped the climate recover in that part of the world.